The present invention may relate to methods and systems for controlling combustion dynamics in the combustor of a gas turbine and may particularly relate to methods for controlling combustion dynamics for variable fuel gas composition and temperature based on actual calculated fuel flow to the combustor and heat input to the gas turbine.
Industrial-based turbines are often gas-fired and are typically used at power plants to drive generators and produce electrical energy. FIG. 1, for example, schematically illustrates a simple cycle, single-shaft, heavy-duty gas turbine, generally designated 10. The gas turbine comprises an axial flow compressor 12 having a rotor shaft 14. Air enters the inlet of the compressor at 16, is compressed by the axial flow compressor 12 and then is discharged to a combustor 18, where fuel such as natural gas is burned to provide high-energy combustion gases which drive the turbine 20. In the turbine 20, the energy of the hot gases is converted into work, some of which is used to drive the compressor 12 through shaft 14, with the remainder being available for useful work to drive a load such as a generator 22 by means of rotor shaft 24 for producing electricity. The heat exhaust from the turbine is illustrated at 26 and may be used for other purposes, for example, in a combined cycle system. Additionally, there is illustrated a heat exchanger 28 for heating the fuel inlet to the combustor 18 in accordance with the present invention.
A current method of heating the fuel gas is to take intermediate pressure (IP) feedwater from intermediate pressure economizer in the heat recovery steam generator (HRSG) and pipe it into the performance heat exchanger. FIG. 2 schematically illustrates the current method for heating the fuel gas in a simple cycle, single-shaft, heavy-duty gas turbine. Generally, inputs to the turbine include fuel gas 202 and air 204, and outputs include electrical energy 206. Fuel gas 202 enters the system via conduit 210 and may be split at valve 212 into conduits 214 and 216. Via conduit 214 fuel gas enters fuel gas saturator 218, in which the fuel gas is moisturized. Other inputs to fuel gas saturator 218 include water, which enters via conduit 220. Unused water exits the fuel gas saturator 218 via conduit 222, and moisturized fuel gas exits the fuel gas saturator 218 via conduit 224. Via conduits 216 and 224, moisturized and unmoisturized fuel gas are mixed in mixer 226 and fed into heat exchanger 230, which heats the fuel gas prior to introduction into turbine 240 via conduit 232.
Air 204, via conduit 234, enters compressor 236, where it is compressed then is discharged via conduit 238 to turbine 240. Turbine 240 includes a combustor (not shown) where the fuel gas is burned in the presence of air to generate heat and generates electricity by driving a generator (not shown). Electrical energy 206 exits turbine 240 via carrier 250. Exhaust exits the turbine 240 via conduit 242, which connects to HRSG 244. IP feedwater exits HRSG 244 via conduit 246, which introduces the IP feedwater into heat exchanger 230, where it heats the feed gas. After heating the feed gas, the IP feedwater exits heat exchanger 230 via conduit 248. High pressure (HP) feedwater from the intermediate pressure economizer in HRSG 244 exits HRSG 244 via conduit 245, which transports the HP feedwater so that it can heat a series of drums 247 (e.g., low pressure, intermediate pressure, and high pressure).